1. Field of the Invention
The present invention relates to an exposure method and an exposure apparatus that are used in manufacturing microdevices through the use of photolithography and used for exposing a substrate by projecting a pattern formed in a mask (hereinafter called a mask pattern) onto a plurality of regions in the substrate one by one by means of a scanning system.
2. Description of the Related Art
To manufacture microdevices by photolithography, a mask pattern is projected through an optical projection system onto a substrate on which a photoresist layer is formed, and the substrate is exposed by the light patterned by the mask pattern. A scanning exposure (lithography) apparatus and a step-and-scan exposure apparatus are known as exposure apparatuses used for such an exposure.
The scanning exposure apparatus is operated such that a portion of the mask pattern is projected onto the substrate through the optical projection system, and the mask and the substrate are moved in synchronization with each other, so that an exposure region in which a portion of the mask pattern is projected and exposure is performed is shifted. As a result, the entire mask pattern is projected onto the substrate, and the substrate is exposed by the light corresponding to the entire mask pattern. To shift the exposure region on the substrate for projecting the entire mask pattern onto the substrate is hereinafter called scanning. A direction in which the exposure region is shifted with respect to the substrate is hereinafter called a scanning direction. Exposure using a large-sized mask pattern is achieved through the use of the scanning exposure apparatus.
The step-and-scan exposure apparatus is operated to repeatedly perform exposure by scanning similar to that performed by the above-mentioned scanning exposure apparatus and a step-by-step movement (step) of the substrate. A region onto which the entire mask pattern is projected by a single scanning is hereinafter called a shot. According to the step-and-scan exposure apparatus, a plurality of shots are defined for a single substrate, and exposure based on the mask pattern is performed for each of the shots. Such step-and-scan exposure apparatuses are disclosed in, for example, the Published Unexamined Japanese Patent Application Heisei 11-251228 (1999), the Published Unexamined Japanese Patent Application Heisei 8-306610 (1996), the Published Unexamined Japanese Patent Application Heisei 10-125589 (1998), the Published Unexamined Japanese Patent Application 2002-246291, and the Published Unexamined Japanese Patent Application 2002-175962.
The Published Unexamined Japanese Patent Application Heisei 11-251228 discloses a technique in which the scanning directions of adjacent shots are made opposite to each other, and fine adjustment of the locations of the mask and the substrate is performed, referring to alignment compensation values that are different between the scanning directions.
The Published Unexamined Japanese Patent Application Heisei 8-306610 discloses a technique in which the scanning directions of two exposures performed for one region of the substrate are made to be the same, wherein one of the two exposures is performed through the use of a first mask pattern that proceeds, and the other of the two exposures is performed through the use of a second mask pattern that follows.
The Published Unexamined Japanese Patent Application Heisei 10-125589 discloses a technique in which, to perform exposure through the use of a specific mask pattern in a single shot, if exposure using another mask pattern has been previously done in the shot, alignment between the mask and the substrate is performed using data of the scanning direction employed at the previous exposure using the other mask pattern.
The Published Unexamined Japanese Patent Application 2002-246291 discloses a technique in which, to transfer a specific pattern to a substrate, exposure in a single shot is performed for each of a plurality of pattern divisions obtained by dividing the specific pattern, and a plurality of shots of the pattern divisions are united to transfer the specific pattern, while the directions of scanning for exposure for the respective pattern divisions are made to coincide with one another.
As disclosed in the Published Unexamined Japanese Patent Application 2002-175962, the step-and-scan exposure apparatus incorporates: a detection means for detecting the location of the surface of the substrate along the direction of optical axis of the optical projection system; and a means for adjusting the location of the substrate along the direction of optical axis of the optical projection system, based on the result of detection by the detection means, so that the image of the mask pattern is focused on the surface of the substrate. The step-and-scan exposure apparatus performs such adjustment before exposure in each shot.
The Published Unexamined Japanese Patent Application 2002-175962 discloses a technique that utilizes a multipoint focus position detection system capable of detecting a plurality of measurement points on the substrate as the above-mentioned detection means. This technique enables selection among the measurement points.
One of microdevices manufactured by photolithography is a thin-film magnetic head slider used in a magnetic disk drive. The slider has: a medium facing surface that faces toward a recording medium; and a thin-film magnetic head element disposed near the medium facing surface. A widely used type of thin-film magnetic head element is a composite thin-film magnetic head element that has a layered structure in which an induction-type electromagnetic transducer for writing and a magnetoresistive (MR) element for reading are stacked.
Typically, the thin-film magnetic head slider is manufactured through a method that will now be described. First, a number of thin-film magnetic head elements aligned in a plurality of rows are formed on a single substrate. In the process of forming the head elements, photolithography is employed to pattern various layers making up the head elements. Next, the substrate including the head elements are cut so as to form a substructure to be processed (hereinafter called a bar) in which portions to be sliders (hereinafter called slider portions) each including one of the head elements are aligned in a row, or to form a substructure to be processed (hereinafter called a block) in which slider portions are aligned in a plurality of rows. Next, if bars are formed by cutting the substrate, processing such as lapping is performed for each of the bars on all the slider portions the bar includes so as to form the medium facing surfaces of all the slider portions the bar includes. Next, the bar is cut and divided into the sliders. If blocks are formed by cutting the substrate, processing such as lapping is performed for each of the blocks on a row of the slider portions located at an end of the block so as to form the medium facing surfaces of the slider portions of the row located at the end of the block. Next, a bar made up of the row of slider portions is separated from the block, and the bar is further cut and divided into the sliders.
According to the above-described method of manufacturing the thin-film magnetic head slider, the medium facing surfaces are formed for a plurality of slider portions aligned in a row in the state of bar or block. In this step of forming the medium facing surfaces, it is required that the MR heights of the thin-film magnetic head elements aligned in the row all fall within a permissible range. The MR height is the length (height) from an end of the MR element closer to the medium facing surface to the opposite end. The step of forming the medium facing surfaces includes the step of lapping the medium facing surfaces. The MR heights are adjusted by the amount of lapping the medium facing surfaces. Such a method of manufacturing the thin-film magnetic head slider is disclosed in each of the Published Unexamined Japanese Patent Application Heisei 11-316928 (1999) and the Published Unexamined Japanese Patent Application 2001-126226, for example.
Reference is now made to FIG. 24 to describe two problems that arise when the thin-film magnetic head sliders are manufactured as described above, wherein a step-and-scan exposure apparatus is employed in the step of forming a number of thin-film magnetic head elements on a single substrate. FIG. 24 illustrates an example of positional relationship between a circular-plate-shaped substrate 201 and shots 202. In FIG. 24, the shots 202 are expressed as forty-four rectangular regions that are identical in size wherein at least one of the sides thereof is indicated with a broken line. In FIG. 24, each of ten rectangular regions 203 surrounded by solid lines indicates a range to be a single block. A portion of the substrate 201 located in each of the regions 203 is to be a single block. Each of the regions 203 includes a row of four shots 202. In FIG. 24, the regions 203 are indicated with hatching for convenience. A mask pattern to be projected onto each of the shots 202 includes a pattern corresponding to a plurality of thin-film magnetic head elements. Therefore, a plurality of slider portions are formed in a portion of the substrate 201 corresponding to a single shot 202.
The first problem results from the fact that some of the shots 202 have portions located outside the edge of the substrate 201. Such shots 202 are hereinafter called edge shots and indicated with 202E. If one or more shots 202 correspond to a single microdevice, portions of the substrate 201 corresponding to the edge shots 202E are not used for manufacturing the microdevice. However, when thin-film magnetic head sliders are manufactured, each of the shots 202 corresponds to a plurality of thin-film magnetic head sliders. Therefore, even the portions of the substrate 201 corresponding to the edge shots 202E could be used for manufacturing the head sliders. According to related art, however, it is difficult that the image of a mask pattern is correctly focused on the surface of the substrate 201 in the edge shots 202E. The reason will now be described. As described above, a step-and-scan exposure apparatus incorporates: a detection means for detecting the location of the surface of the substrate along the direction of optical axis of an optical projection system; and a means for adjusting the location of the substrate along the direction of optical axis of the optical projection system, based on the result of detection by the detection means, so that the image of the mask pattern is focused on the surface of the substrate. The step-and-scan exposure apparatus performs such adjustment before exposure in each of the shots 202. However, in the edge shots 202E, it is impossible to correctly detect the location of the surface of the substrate 201 since portions of the edge shots 202E are located outside the edge of the substrate 201. As a result, it is impossible for the edge shots 202E that the image of the mask pattern is correctly focused on the surface of the substrate 201. Consequently, variations in width of layers patterned based on the mask pattern are increased.
The first problem not only applies to cases of manufacturing thin-film magnetic head sliders but widely applies to cases in which a plurality of microdevices are formed in a portion of the substrate corresponding to a single shot.
The second problem results from the fact that a plurality of shots 202 (four shots 202 in the example shown in FIG. 24) correspond to a single bar or block. That is, in the method of manufacturing the thin-film magnetic head sliders, the medium facing surfaces of a plurality of slider portions aligned in a row in a bar or block are formed at the same time. Therefore, if there are great variations in location along the vertical direction of FIG. 24 among a plurality of shots 202 located in a single region 203 corresponding to a single block, there result great variations in MR height among a plurality of thin-film magnetic heads included in the slider portions whose medium facing surfaces are formed at the same time. For the step-and-scan exposure apparatus, even if the locations of a plurality of shots aligned in a row are predetermined such that the locations thereof along the direction of scanning coincide with one another, there may be variations among the locations of the shots after exposure along the direction of scanning, since the mechanical precision of the step-and-scan exposure apparatus is not perfect. Furthermore, the step-and-scan exposure apparatus is typically designed such that, to reduce the process time, the directions of scanning are opposite to each other in respective two of the shots adjacent to each other in the direction orthogonal to the directions of scanning. In this case, it is more likely that there is a great variation in the locations of the adjacent two shots along the direction of scanning after exposure, compared with the case in which the directions of scanning in the adjacent two shots are identical. As a result, when the directions of scanning are opposite to each other in the adjacent two shots, in particular, there result great variations in locations along the vertical direction of FIG. 24 among a plurality of shots 202 corresponding to a single block, and variations in MR height are thereby increased, too.
It is impossible to solve the first problem by any of the techniques disclosed in the Published Unexamined Japanese Patent Application Heisei 11-251228, the Published Unexamined Japanese Patent Application Heisei 8-306610, the Published Unexamined Japanese Patent Application Heisei 10-125589, and the Published Unexamined Japanese Patent Application 2002-246291. According to the technique disclosed in the Published Unexamined Japanese Patent Application 2002-175962, when the edge shots 202E are exposed, the location of the surface of the substrate 201 is detected by choosing measurement points only located within the region inside the edge of the substrate 201. It is thereby possible that the image of the mask pattern is correctly focused on the surface of the substrate 201. However, this technique has a problem that complicated processing is required for detecting the location of the surface of the substrate 201. Furthermore, the second problem is not taken into consideration in the Published Unexamined Japanese Patent Application Heisei 11-251228, the Published Unexamined Japanese Patent Application Heisei 8-306610, the Published Unexamined Japanese Patent Application Heisei 10-125589, the Published Unexamined Japanese Patent Application 2002-246291, and the Published Unexamined Japanese Patent Application 2002-175962.